Process for the production of krypton and xenon



June 2-, 1942. KAHLE 2,284,662

PROCESS FOR THE PRODUCTION OF KRYPTON AND XENON Filed March 12, 195'? 2Sheets-Sheet 2 INVENTOR HEINRICH KAHLE ATTORNEY Patented June 2, 1942PROCESS FOR THE PRODUCTION OF KRYPTON AND XENON Heinrich Kahle,Hollriegelskreuth, near Munich,

Germany Application March 12, 1937, Serial No. 130,428 In. Germany March23, 1936 3 Claims. (Cl. 23-209) This invention relates to a process forthe production of krypton and xenon, and particularly to the recovery ofkrypton and xenon from gas mixtures containing hydrocarbons.

Various processes have been proposed for recovering the rare gaseskrypton and xenon, in particular from the air through enrichment in anoxygen-containing atmosphere. However, due to the fact that hydrocarbonconcentrations occur simultaneously with the rare gases, the processingof the crude concentrate is made extraordinarily difficult andexpensive. Particularly when the concentrate is to be directly processedto recover the pure rare gases, the most careful removal of even theslightest traces of hydrocarbons, which are present in small percentagesin a large volume of gas, is necessary due to the high degree ofenrichment effected. Despite all precautionary measures having beentaken, this method of operation has nevertheless resulted in someaccidents.

Therefore the principal object of the present invention is to provide amethod for recovering krypton and xenon by which the above difficultiesare fundamentally eliminated.

Other objects of the present invention are: to provide a method forrecovering krypton and xenon by enrichment in an atmosphere free ofoxygen; for recovering krypton and xenon from i oxygen-free gasmixtures; for separating krypton from a gas mixture by washing with aliquefied gas having a higher boiling point than krypton and in whichkrypton is soluble.

These and other objects of the invention and the novel features thereofwhich achieve these objects will become evident from the followingdescription taken in connection with the accompanying drawings, inwhich:

Fig. 1 is a diagrammatic view partly in section a of an apparatus forpracticing the method of the present invention; and

Fig. 2 is a similar view of another form of the apparatus.

Fig. 3 is a diagrammatic view partly in section of an apparatus for thefurther treatment of a rare gas concentrate obtained by means of apreliminary rectifying apparatus such as shown in Fig. 1.

In accordance with the invention the enrichment of the rare gaes,krypton and xenon is effected in a reducing, i. e., oxygen-freeatmosphere. For this purpose there is used for the production of kryptonand zenon either an oxygen-free byproduct gas or if, as in airseparation, the preliminary enrichment of these rare gases in anoxygen-containing atmosphere cannot be prevented, the presence of oxygenis excluded during the processing of the raw mixture.

The new process is best more fully explained in connection with variouspreferred examples. In the specification and claims, it is to beunderstood that the word-krypton is intended to include both the raregases krypton and xenon collectively unless otherwise set forth.

If nitrogen is utilized in a process for ammonia synthesis, whichnitrogen has been produced from air by the chemical elimination of theoxygen, or if the hydrogen for the synthesis is produced by thegasification of fuels with oxygen, then 'the synthesis gases containkrypton and xenon which become enriched in these gases by recyclingthrough the process. Even though such enrichment can proceed to thepoint where the krypton content is greater than that in the air, noattempt has heretofore been made to use such gas mixtures for theproduction of krypton, due to the fact that their separation as comparedto air separation is exceedingly more difficult due to their complicatedcomposition.

According to the present invention, gas mixtures of the type such as theresidual gases resulting from the synthesisof ammonia are used for theproduction of krypton in order to be able to carry out the eniichment ofthe krypton in an oxygen-free atmosphere.

This method of recovering krypton and xenon will be more fully explainedby reference to Fig. 1, in which periodically reversible coldaccumulators Hi and I! of known variety have their warn ends connectedto a reversing valve H by conduits l3 and I4 and their cold endsconnected to reversing valve l5 by conduits l6 and H. The gas mixture tobe treated is conducted to valve l I by a conduit l8 and flows throughone or the other of the accumulators to reversing valve l5 from which itis conducted by conduit I9 to the lower portion of a separating column20 where it is washed by countercurrent contact with a reflux liquidpassing downward through the column. The column is provided withrectifying trays 2| to improve the contact. The lower portion or kettle22 of the column is provided with a heating coil 24 and the upperportion is provided with a condenser 25 which is surrounded by a coolingjacket 23. The condenser may be provided with a dome vent conduit 26having a stop valve 26'.

The treated gas passes out of the column at its upper portion through aconduit 21 which connects to the reversing valve IS. The treated mixtureafter passing through the accumulators where it gives up itsrefrigeration, passes to valve II and is conducted away from the valveby cond'uit 28i Any desired means for heating the coil ing coil 24 wherethe nitrogen liqucfles and heats the liquid in kettle 22. The liquidnitrogen is conducted through conduit 34 to the jacket 23 being expandedthrough the expansion valve 35 interposed in conduit 34. The liquidnitrogen in jacket 23 vaporizes due to the absorption of heat from thegases entering the condenser 25 and the vapors produced are drawn off byconduit 36 which conducts them to the other pass of heat exchanger 33.Here the vapors are heated by absorbing heat from the compressednitrogen flowing in the opposite direction. The suction conduit 31 ofthe compressor conducts the warmed vapors out of the heat exchanger 33so that the compressor may recompress them and recycle the nitrogen. Theamount of heat delivered to the coil 24 may be regulated by providing asuitable controllable bypass around the .heat exchanger 33. Thetemperature of the condenser 25 may be controlled by regulating thepressure under which the nitrogen evaporates in the jacket 23. The raregas containing concentrate that collects in kettle 22 is withdrawnthrough a conduit 38 controlled by valve 38'.

The residual gases from the synthesis of ammonia for example, are cooledin the periodically alternated cold accumulators I0 01'' I2 incountercurrent heat exchange with the krypton-freed gas and thenintroduced into the rectification column 20. A portion oi the gasmixture passing up the column is liquefied in condenser 25, tricklesdownward in column 20 in countercurrent relation to the rising gas andthereby washes out the krypton which collects in the liquid in kettle 22at the bottom of the column. Th kettle 22 is heated by means of anauxiliary gas, e. g. nitrogen which is liquefied under pressure in thecoil 24 and thereupon after expansion through valve 35 is evaporated bycooling condenser 25. The auxiliary gas is preferably conducted incyclic fashion, i. e., after its evaporation in jacket 23 it is heatedin countercurrent relation with itself in exchanger 33 and aftercompression in the compressor 29 and cooling is again employed forheating the column 2i0.

The recovery of the krypton from the gas mixture can. now .be effectedby two different methods. The one method of operation according to theinvention is analogous to the known scrubbing processes in which liquidsare utilized whose boiling points are lower than that of krypton. Forsuch a method there is condensed in condenser 25 principally nitrogenand a small quantity of methane to form the reflux liquid. Under thesecircumstances the gas mixture is separated into nitrogen-containinghydrogen, which is withdrawnthrough conduit 21, and into a mixture ofthe hydrocarbons collecting in kettle 22 which contains the krypton. Thekrypton concentrate is thereupon withdrawn through conduit 33.

Another method of krypton rec'overy according to the invention iscontrary to any process previously employed, in that solvents forkrypton are employed as washing media which are less volatile thankrypton. It was found that hydrocarbons such as in particular, propaneand the like, show a high solvent power and an extensive miscibilitywith krypton. Use is made of this discovery in a method of operationcarried out in a form' of apparatus which will be described inconnection with Figure 2 where a mixture of hydrocarbons is liquefied atthe foot of a separating column and is conducted as washing medium tothe head of the column.

In the form of apparatus shown in Fig. 2, the rare gas containingmixture cooled by passage through the cold accumulators I0 or I2 isconducted to an expansion engine I9 wherein the gas mixture is expandedto a lower pressure with the production of external work so as toprovide refrigeration to counteract heat losses. The expanded mixture isconducted by conduit I I9 from the expander to a column I20 where itpasses upward in intimate countcrcurrent contact with reflux liquidpassing down the column. The treated gas passes from the top of thecolumn I20 through the conduit 2'! to the valve I5 which in the positionshown passes the cold treated gas to accumulator I2 where it depositsits refrigeration. The treated gas flows out of accumulator I2 throughconduit I4 to valve II which is in the position to pass the treated gasto discharge conduit 28. The incoming rare gas containing mixture inthis position of the valves is seen to flow through accumulator I0 to becooled and to be passed to conduit I9 by valve I5. When the valves IIand I5 are reversed the flow through the accumulators is in the oppositedirection, the treated mixture flowing through accumulator I0 and theincoming mixture flowing through accumulator I2. In this form ofapparatus, reflux is provided by supplying a hydrocarbon gas which maypreferably be a member of the par'afline series, for example, propaneunder pressure through a conduit I30'to the heating coil I24 disposedwithin the lower kettle I22 of the column I20. From the heating coilI24, where the propane is cooled and liquefied by heating the liquid inkettle I22, the propane is conducted as reflux liquid to the upper trayI2I of the column after passage through the expansion valve I35. Thecold liquid propane, passing down the column dissolves krypton andcarries it down to the kettle I22 becoming more concentrated in kryptonfrom the synthesis of ammonia are treated. To-

this group belong all gas mixtures which are produced through thegasiflcation of fuels by the utilization of air or oxygen, and whichgenerally contain hydrogen as their principal component, such as forexample, the gases used for coal hydrogenation or for syntheses, or theresidual gases from the hydrogenation or syntheses.

It has been proposed to recover krypton from gas mixtures such as fluegas which are richer in nitrogen than air. These gases, however,

always contain residual oxygen which becomes enriched together with thekrypton and the hydrocarbons, so that the danger of explosion In an airseparation plant, air is subjected to rectification by washing withliquid air in a rectifying column and the washed liquid at the foot ofthe column is evaporated to such a degree only that, in addition to theprincipal component oxygen, it contains approximately 1% krypton and amaximum. of 1% hydrocarbon. This mixture or concentrate is withdrawnfrom the separation plant, evaporated, and in accordance with thepresent invention, the oxygen content thereof is completely reacted withan excess of hydrogen. The oxygen-free concentrate thus produced is thensubjected to further enrichment. Pure hydrogen is not required for thisconversion, but it is possible, however, to utilize other hydrogencontaining gases such, for example, as conversion hydrogen whichcontains nitrogen, carbon monoxide or hydrocarbons. Likewise, fractionsfrom the separation treatment of coke-oven gas or of hydrocarbonmixtures can be employed for this purpose.

One form of an apparatus for carrying out this further treatment isillustrated in Figure 3. As shown, the rare gas concentrate containingoxygen, produced by an air separation apparatus or by treatment in anapparatus such as that illustrated in Figure 1 from which it iswithdrawn through valve 38', enters the apparatus shown in Figure 3through conduit 38". The mixture is introduced as shown, into thechamber of a reactor 39, preferably by means of nozzle 40. A combustiblegas, for example hydrogen, is conducted to nozzle 40 through a conduit4| for admixture with the oxygen-containing mixture. This combustiblegas is preferably added in excess of the amount necessary for thecomplete combustion of the oxygen of the mixture and the products ofcombustion pass by means of conduit 42 into a condenser 44. Heat evolvedby the combustion reaction may be used to generate steam in a boiler 43.Condenser 44 is preferably enclosed by a water jacket 45 to cause thecondensible products of combustion such as water, to collect in a liquidseparator 41 into which the products pass through a conduit 46. Theremaining gas mixture, including gaseous products of combustion, isconducted from separator 41, by means of a conduit 48 into the bottom ofan alkaline washing tower 49 where the gases pass upwardly andcountercurrently to a descending stream of caustic solution or othermedium suitable for removing carbon dioxide. For example, incomingwashing liquid may enter through a conduit 50 and after falling throughthe tower 49, which is preferably packed to increase interfacial surfacecontact between liquid and gas, the liquid containing carbon dioxide iswithdrawn at 5|. Such liquid may be treated to remove carbon dioxideafter'which, if desired, it may be recirculated to the top "of the tower49. The washing step efiected in tower 49 obviously, may be omitted ifthe gas mixture originally contained -no hydrocarbons and pure hydrogenis used for the combustion. By means of a conduit 52 the washed gas,comprising in addition to the rare gases and hydrocarbons, the morevolatile gases such as hydrogen, nitrogen and carbon monoxide, isconveyed from tower 49 to the inlet of a compressor 53 where it iscompressed to a desired pressure. The compressed gas passes through adischarge conduit 54 to an absorber 55 which contains a dehydratingagent such as caustic, whereby the last traces of water are removed.

The dry gas then passes by means of conduit 56, through a heat exchanger51, whereby it is cooled to a low temperature, and conducted into arectifying column 58 through a heating coil 59 in the base of thecolumn, wherein the gas is liquefied by heat exchange with liquid in thebase of the column. From the coil 59, the substantially liquefied gaspasses through a conduit BI] and an expansion valve 6! and enters onto adesired plate of the lower portion of fractionating column 58. The lowboiling gaseous constituents pass up the column, and into contact with areflux condenser 62 which condenses low boiling constituents to providea sufficient amount of reflux to effect the separation of the rare gasfrom the gas mixture. The low boiling constituents such as hydrogen andnitrogen passing through reflux condenser 62 are discharged through aconduit 63 to heat exchanger 51 to chill the incoming gas enteringthrough conduit 56 and leave the apparatus by a conduit 54. Refluxcondenser 62 may be refrigerated in any suitable manner, for example asindicated in Figure 1 by means of a closed nitrogen circuit, whereby theliquid nitrogen enters through a conduit 65 and upon evaporation thenitrogen leaves through a conduit 66. The concentrated liquefied raregases collecting at the base of the column are withdrawn therefromthrough a conduit 6'! by control 7 valve 68.

The scrubbing of the rare gases from the concentrate can be effected ina particularly simple manner by washing the'gas mixture either withliquid substances more volatile than krypton, such as relativelymorevolatile nitrogen or carbon monoxide, or with less volatile substances,such as relatively less volatile propane as previously described. Thehereby resulting liquid, which is rich in krypton and xenon, can then beprocessed to pure krypton.

The advantages of the new process include not only the absoluteexclusion of the dangers caused by the hydrocarbons, but rather alsothat the number of different wash liquids which become available forwashing out the krypton is appreciably increased, since, by means of thepresent process, it is possible for the first time to.employhydrocarbons as washing mediums for the production of krypton.

I claim:

1. Process for producing the rare gases krypton and xenon whichcomprises collecting a concentrate of said rare gases, treating the saidconcentrate with liquid propane to dissolve said rare gases, separatingsaid liquid propane containing said rare gases from the remainder ofsaid concentrate, and separating the propane from the krypton and xenon.

2. Process for producing the rare gases krypton and xenon whichcomprises collecting a concentrate of said rare gases, the proportion ofkrypton in said concentrate being greater than the proportion of xenon,treating such concentrate with a iiquid comprising liquefied propane todissolve said rare gases, separating said liquid containing said raregases from the remainder of said concentrate, and separating said liquidfrom the krypton and xenon.

3. Process for the production of krypton and xenon from an oxygencontaining starting gas containing said rare gases which comprisesforming a rare gas concentrate by chemical conversion of the entireoxygen content of said starting gas, removing the conversion products,

further enriching the rare gas content by effecting a chemicalconversion of components other than said rare gases, removing theproducts of said second conversion, treating said concentrate withliquid propane to dissolve said rare gases, separating said liquidpropane containing said rare gases from the remainder of saidconcentrate, and separating said propane from the krypton and xenon.

HEINRICH KAHLE.

